An optical communication network system is designed before an operation of communication services, based on preset system conditions such as, for example, fiber parameters, a signal modulation format, a bit rate, a fiber input optical power. However, since actual parameters cannot be measured before the operation, values considering a margin are used for the design. However, since it is difficult to estimate an appropriate margin, for example, an excessive margin may be set. Therefore, a design value inferior to an actual system performance may be set, which may result in a lack of a system performance such as, for example, a reduction of a transmission distance.
In order to overcome this problem, various methods are under consideration including a first method that uses information of optical fibers and optical signals under operation to determine whether or not to permit a transmission of the entire span and a second method that measures the quality of optical signals under operation, stores the measured signal quality in a database, and uses the stored signal quality to design a system.
In the first method, a probability distribution of a crosstalk amount of a four wave mixing (FWM) of each span is calculated, and a probability distribution of a crosstalk amount of an FWM of the entire span is calculated based on the probability distribution of each span. In addition, from the probability distribution of the crosstalk amount of the FWM of the entire span, it is determined whether or not to permit a transmission of the entire span based on a predetermined criterion. However, while the first method requires fiber parameters, it is difficult to measure actual fiber parameters.
In contrast, the second method uses a case-based reasoning to estimate a signal quality. In the second method, known system conditions such as, for example, the number of wavelengths and an input power are stored in a database in association with signal qualities such as, for example, an optical signal to noise ratio (OSNR) and an error vector magnitude (EVM). Then, a signal quality of the system condition similar to a system condition of a wavelength path of an estimation target at which the signal quality is estimated, is retrieved from the database, and the retrieved signal quality is estimated as a signal quality of the wavelength path of the estimation target. The wavelength path labels the wavelength to transmit the optical signal.
FIG. 38 is an explanatory view illustrating one example of each wavelength path in a transmission system. The transmission system illustrated in FIG. 38 includes, for example, nodes A to G and also includes a span for each wavelength path λ. For example, a wavelength path λ1 corresponds to a path between the node A and the node C and is implemented with a span A-B and a span B-C.
A wavelength path λ2 corresponds to a path between the node B and the node E and is implemented with a span B-C, a span C-D, and a span D-E. A wavelength path λ3 corresponds to a path between the node A and the node G and is implemented with a span A-B, a span B-C, a span C-D, a span D-E, a span E-F, and a span F-G. A wavelength path λ4 corresponds to a path between the node D and the node G and is implemented with the span D-E, the span E-F, and the span F-G. For convenience of description, it is assumed that the wavelength paths λ1, λ2, and λ4 are wavelength paths under operation, the wavelength path λ3 is a wavelength path of an estimation target, and signal qualities of the wavelength paths λ1, λ2, and λ4 are stored in a database. The wavelength path of an estimation target is, for example, a path newly added in the transmission system or a path requiring an estimation of a signal quality such as, for example, a path of a switching destination at the time of path switching.
In the second method, for example, when the wavelength path λ3 of the estimation target is estimated, the signal qualities of the wavelength paths λ1, λ2, and λ4 stored in the database may be used to estimate the signal quality of the wavelength path λ3. That is, when there exists a wavelength path of the estimation target of the same span as a wavelength path under operation, the signal quality of the wavelength path under operation stored in the database is approximate to the signal quality of the wavelength path of the estimation target. As a result, the approximate signal quality of the wavelength path under operation may be used to estimate the signal quality of the wavelength path of the estimation target.
Related technologies are disclosed in, for example, Japanese Patent No. 4861960.
Related technologies are disclosed in, for example, Antonio Caballero et al., “Experimental demonstration of a cognitive quality of transmission estimator for optical communication systems,” Opt. express, vol. 20, no. 26, B64-B70.